<img src="http://img11.360buyimg.com/da/g14/M07/01/0E/rBEhVlNhh8wIAAAAAADmFBLo1twAAM26gOmCgYAAOYs716.jpg">
<script>
var img = document.getElementsByTagName('img')[0]
var width = getWH(img, 'width') // 690
</script>

<img width="400" src="http://img11.360buyimg.com/da/g14/M07/01/0E/rBEhVlNhh8wIAAAAAADmFBLo1twAAM26gOmCgYAAOYs716.jpg">
<script>
var img = document.getElementsByTagName('img')[0]
var width = getWH(img, 'width') // 400
</script>

<img width="400" src="http://img11.360buyimg.com/da/g14/M07/01/0E/rBEhVlNhh8wIAAAAAADmFBLo1twAAM26gOmCgYAAOYs716.jpg">
<script>
function getNaturalWidth(img) {
var image = new Image()
image.src = img.src
var naturalWidth = image.width
return naturalWidth
}
var img = document.getElementsByTagName('img')[0]
getNaturalWidth(img) // 690
</script>

function getImgNaturalDimensions(img, callback) {
var nWidth, nHeight
if (img.naturalWidth) { // 現代瀏覽器
nWidth = img.naturalWidth
nHeight = img.naturalHeight
} else { // IE6/7/8
var imgae = new Image()
image.src = img.src
image.onload = function() {
callback(image.width, image.height)
}
}
return [nWidth, nHeight]
}